Lamphouse with premixing

ABSTRACT

In a lamphouse assembly, light energy from several different individual light sources, each providing a primary color, is premixed and then introduced into a main mixing chamber through a rod screen, there being one such screen for each premixing chamber. The main mixing chamber is provided with an upwardly recessed roof and is further configured so that a highly diffused and uniform field of light is directed downwardly through the emission opening onto the printing paper.

United States Patent [72] Inventors Roy A. Clapp Coon Rapids; Haven Douglas Noble, Robbinsdale; Douglas L. l-lavlland, Minneapolis, all of Minn.

[21] Appl. No. 798,916

[22] Filed Feb. 13, 1969 [45] Patented Dec. 28, 1971 [73] Assignee Nord Photo Engineering, Inc.

Minneapolis, Minn.

[54] LAMPHOUSE WITH PREMIXING 20 Claims, 7 Drawing Figs.

[52] 0.5. Ci. 355/37, g 355/88 [51] Int." .....G03b 27/54 [50] Field 01 Search 240/3.1, 41.35; 355/32,,37, 52, 88,113,119, 36; 353/29, 31, 84

[561 References Cited UNITED STATES PATENTS 1,782,551 11/1930 Sullivan 240/411 2,321,099 6/1943 Naysmith 240/5111 2,943,554 7/1960 Kastner 355/111 3,164,056 1/1965 Wick et al.. 355/37 3,316,804 5/1967 Weisg1ass.. 240/4601 X 3,492,070 1/1970 Zahn 355/37 Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard M. Sheer Attorney-Bugger, Peterson, Johnson 81. Westman ABSTRACT: In a lamphouse assembly, light energy from several different individual light sources, each providing a primary color, is premixed and then introduced into a main mixing chamber through a rod screen, there being one such screen for each premixing chamber. The main mixing chamber is provided with an upwardly recessed roof and is further configured so that a highly diffused and uniform field of light is directed downwardly through the emission opening onto the printing paper.

LAMPHOUSE WITH PREMIXING BACKGROUND OF THE INVENTION 1. Fieldof the Invention I This invention relates generally to color photographic enlarging, and pertains more. particularly to a lamphouse utilizing premixing techniques.

2. Description of the Prior Art I The use of an integrating or mixing chamber is of course not new. Various attempts havebeen made in an effort to obtain a high. level of light diffusion with the proper spectral content. One prior art arrangement has employed a light integrating or mixing chamber having a rectangular plane and tapering sides with multiple admitting ports in the sides, the admitting ports having the individual color filters positioned thereover so that the light injected'through the various ports will possess different colors, namely, red, greenand blue. While. this arrangement permits the light integrating or mixing chamber to serve the dual purpose of mixing different colored light energies and at the same time rendering the resulting illuminant diffuse, there have been practical difficulties attending this construction, one prominent difficulty being that some areas of the negative are more strongly illuminated than others, thereby causing spots to appear in the print.

One effort to overcome the above difficulty has involved the use of small reflectors located within the integrating or mixing chamber which subdivide the beams of light that are injected, but such reflectors interfere with the internal reflective action between the various surfaces of the chamber with a concomitant reduction in efficiency. Such approaches still fail to obviate the objectional color mottling. Still further, any attempt to increase the size of emission opening with respect to the overallinterior surface has resulted in a less uniform distribution of light.

SUMMARY OF THE INVENTION An important general object of the invention is to provide a highly diffuse and uniform light field that is directed through the color negative onto theprinting paper. Thus, an aim of the invention is to provide both the means for obtaining a good color balance and forcontrolling the density of the resulting print. In other words, the instant invention enables the making of enlarged color prints of excellent quality.

Another object of the invention is to provide a photographic enlarger, particularly for the making of color prints, that is exceedingly simple, thereby allowing novices with only a minimum of instruction to produce professional prints. In this regard, the adjustments needed are-very simple to make and eliminate completely the need for any calculations that have proved so bothersome in the past.

Another object of the invention is to avoid having to insert and remove filters. Also, the invention avoids the building of neutral density and obviates the problem of fading of filters or loss of calibration.

A still further object of the invention, which is very important as far as the overall quality of the resulting print is concerned, is the minimizing of the adverse effects normally occurring by reason of dust and scratches that have heretofore been reproduced in the print.

Yet another object is to enable the operator to save time in the making of finalrprints after viewing preliminary tests, and also to reset the controls in an accurate manner once he has assured himself that the proper quality print has initially been made.

A still further object of the invention is to reduce the amount of reflective surface'area within the mixing chamber, thereby allowing the chamber to be smaller for a given size of emission opening.

Briefly, the present invention envisages at least one premixing chamber in which light energy from several different sources is initially mixed, each source furnishing light flux within the appropriate spectral range to provide a given primary color. After premixing, the resulting light is then directed through a dispersive or distributing means in the form of a rod screen, and is then further mixedin a main chamber, having the proper shape orconfiguration so that a uniform and diffused light is made available for the actual color printing the colored printing paper. By varying the intensity of each light source on an individual basis, an excellent color balance and control of the print density are achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a front elevational view of a photographic enlarger embodying our invention therein;

FIG. 2 is a view taken in the direction of line 2 -2 of FIG. I for the purpose of illustrating the general layout of the component parts contained within the lamphouse assembly, the top cover and a portion of the roof of the main mixing chamber being removed;

FIG. 3 is a sectional view taken in the direction of line 33 of FIG. 2 for the purpose of illustrating some of the reflective action that takes place within the lamphouse assembly;

FIG. 4 is a sectional view taken in the direction of line 4-4. of FIG. 3;

FIG. 5 is a bottom plan view of the roof for the main mixing chamber, the view being upwardly in the direction of line 5.5 of FIG. 3;

FIG. 6 is a top plan view of the upstanding wall meansforming the lower portion of the main mixing chamber, the view being taken in the direction of line 6-6 of FIG. 3, and FIG. 7 is an enlarged sectional view taken in the direction of line 7-7 of FIG. 3 for the purpose of illustrating with greater particularity the internal arrangement of one of the premixing chambers.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1 of the drawings, a photographic enlarger has been designated generally by the reference numeral 10. The enlarger 10 includes a table I2 having controls 14 and 16 associated therewith that need be only broadly alluded to. Although the printing paper and the supply means for fumishing said paper have not been illustrated, it will be understood that the paper is placed on top of the table 12. A probe 18 appears in FIG. I and this probe is utilized to sense and thereby permit adjustment of the light conditions prior to making a print.

Further included in the enlarger 10 is an upright column or standard 20 having a sheave 22 at the upper end thereof. Entrained about the sheave 22 is a flexible strap 24 that is counterweighted so as to facilitate the raising and lowering of a lamphouse assembly indicated in its entirety by the reference numeral 30. Inasmuch as the lamphouse assembly 30 exemplifies our invention, it will be described in detail hereinafter. However, at this moment attention is directed to a negative holder 32 that is visible in both FIGS. 2 and 3. A conventional bellows 34 extends downwardly from the lamphouse assembly 30 and at the lower end of the bellows is a typical lens 36.

Describing now the lamphouse assembly 30 in detail, it will be seen that the assembly 30 comprises a rectangular cubicle or casing 38. Leading into each end of the cubicle or casing 38 are ventilating hoses 40 for supplying air in order to cool the interior of the cubicle 38, the air entering via slots 42 in the ends of the cubicle. Within the cubicle 38 is a platform 44 adjacent each end, each of the platforms 44 having an opening 46 therein so that the air arriving through the slots 42 can then pass upwardly into the region above the platforms 44 in each instance. Associated with each platform 44 is a partition or divider 48 that extends almost to the top of the cubicle 38 but terminating in a spaced relation therewith so as to provide clearance at 50 for the continued movement of the cooling air. The air traverses general paths denoted by the arrows 5 2.

A plurality of high-intensity lamps 54, such as the watt EJM model lamp manufactured by the General Electric Company, are mounted on the two platforms 44. While the lamps 54 provide white light, still the purpose of each lamp is to furnish light energy that is filtered so as to provide the desired primary color. It will be of assistance, it is believed, to apply specific designations to each grouping of lamps. Therefore, the lamp 54 that has been selected to provide the primary color red has been labeled 54R, the one that is to supply the primary color green has been giventhe reference character 54G and the lamp to furnish the primary color blue has been assigned the reference numeral 548. Hence, it will be appreciated that in the exemplary instance, two sets of lamps 54 are utilized, there being a lamp 54R, 546 and 54B at each end of the cubicle 38.

.As best observed from FIG. 7, filters 56 are associated with the various lamps 54R, 54G and 548. It is by reason of the filters 56 that the actual primary color is produced, the filters being designated specifically by the reference numerals 56R, 56G and 568 to denote the particular primary color that they furnish. Although not essential to an understanding of the invention, but nonetheless essential in actual practice, are heat absorbing filters 58. The desirability of using heat filters is well understood in the art, for they remove infrared energy which adversely affects color-sensitized material, prevents cracking of glass color filters and help to prevent fading of the color filters, especially of the gelatin variety, and also contribute to the stability of such filters.

f prime importance to the realization of the benefits to be derived from our invention is a premixing chamber 60' associated with each trio of lamps. 54. Although appearing in FIG. 2, the construction of each premixing chamber 60 is perhaps best understood from FIGS. 3 and 7. The chamber 60 in each instance includes a top horizontal wall 62, a bottom wall 64, side walls 66 and 68 and angled end walls 70 and 72. The inner surfaces of the walls 62 and 64 should be highly reflective and in actual practice these walls are made from polished aluminum. The light energy from the lamp 54R enters through an opening 74R formed between the vertical edges of the angled end walls 70 and 72, whereas the energy furnished by the lamps 546 and 54B enters the chamber 60 via openings 74G and 748 in the sidewalls 66 and 68, respectively.

It will be helpful to indicate the path that is traversed by the light passing through the chamber 60 with arrows in FIGS. 3 and 7. Since FIG. 3 is a sectional view taken in a vertical plane through the center of our lamphouse assembly, the direction being indicated by the line 3 -3 in FIG. 2, the arrows 76 shown in FIG. 3illustrate the reflective action that the light takes as it is literally bounced between the top and bottom walls 62, 64. In FIG. 7, though, the arrows 76 appear to be following straight nonreflective paths. It will be appreciated that when the light energy is able to follow a direct path without reflection, it does so. However, the efficiency of the mixing action that transpires within each chamber 60 is enhanced by the reflectivity of the inner surfaces provided by the top and bottom walls 62 and 64.

As best viewed in FIG. 7, the light energy represented by the arrows 76 continues and strikes a rod screen 78 residing in a generally vertical plane. The rod screen 78 is composed of cylindrical segments at each side thereof. Hence, the surface designated by the numeral 80a is first impinged upon by the light denoted by the arrows 76 and is dispersed and distributed as it passes through the rod screen 78 so that it leaves the surface 80b on the other side in a random and distributed relation. The randomness of the light exitingfrom the rod screen 78 is indicated by the multidirectional arrows 82. The dispersive role played by the rod screen 78 enhances the resulting degree of diffusion that occurs up to this point.

Having presented the foregoing descriptive information with respect to the premixing chambers 60, attention is now called to a main mixing chamber 84. The mixing chamber 84 is comprised of enclosing wall means which includes upstanding end walls 86, upstanding sidewalls 88 and four angled corner walls 90. It will be well to describe the upstanding end walls 86 with greater particularity; in this regard, each wall 86 is composed of a lower substantially vertical panel 860 and an upper outwardly diverging or inclining panel 86b. Actually,

there is a slight outward taper or divergenceimparted to the sidewalls 88 and this same degree of divergence is incorporated into the lower panels 86a. Hence, the divergence of the end walls 86 increases as far as the panels 86b are concerned. V

Formed in the panels 86b in each instance is a port 92 providing an admitting opening so that the light energy passing through the rod screens 78 will be properly introduced into the main mixing chamber 84. In this regard, it is to be observed from FIGS. 2 and 3, especially the latter, that the ports 92 are inclined, owing to the inclination of the panels 86b in which they are located, and that the lower wall 64 of each premixing chamber just further inward than the upper wall 62. In other words, the upper end of the rod screen 78 is even with the end of the wall 62, whereas the lower wall 64 extends inwardly beyond the lower end of the rod screen. This causes the light that is literally bouncing up and down as it moves through each premixing chamber 60 to be directed upwardly as it enters the main mixing chamber 84. Although the reflective and diffusive action that occurs within the main mixing chamber 84 will not at this stage be fully appreciated, it can be explained that there is an emission opening 94 via which the mixed light energy is abstracted. This opening 94 is formed by an inwardly directed bottom flange 96 integral with the lower edge of each wall 86 and 88. The flange 96 functions as a support for a conventional difiusing plate 98. At the upper edge of the wall means, actually the various walls 86, 88 and 90, is an outwardly directed top flange I00.

Inasmuch as one of the objects of the present invention is to minimize the occurrence of localized areas or spots where a given color predominates, the configuration of the entire mixing chamber 84 is of considerable importance. Contributing to this overall goal, however, is the shape of a roof I02 that overlies the wall means. More specifically, it will be discerned that the roof 102 is formed with a central recess I04 and that the central recess'is composed of upwardly inclining flat panels 104a and l04b. At the upper edges of these flap panels I040, 104b is a horizontal panel I04c. Still further, the central recess 104 includes end panels 104d and l04e. FIG. 5 shows quite clearly the recess configuration and it will be perceived that the end panels are somewhat triangularly shaped (see also the panel 104e visible in FIG. 4). It will be further notedthat a flat marginal section 106 constitutes an integral part of the roof 102, extending completely around the lower edges of the panels 104a, 104b, 104d and 104e. The presence of the flat marginal section I06 not only assists in the downward reflection of light energy but also enables the roof I02 to be releasably held in place with respect to the top flange 100, a plurality of resilient clips 108 (FIG. 4) being employed.

It will be appreciated that the entire interior surface of the main mixing chamber 84 is specular, having applied thereto a coating consisting of, for example, white acrylic latex paint that provides a matte finish which is not only highly reflective but which also contributes to the effective diffusing of the light striking the coated surface. The various omnidirectional arrows labeled 110 give a good idea as to the multiple reflections that take place within the main mixing chamber 84.

The need for a uniform, highly diffused light pattern cannot be stressed too greatly where quality colored prints are to be made. The previously mentioned diffusing plate 98 is placed at the emission opening 94 and the light impinging upon the plate 98, due to the overall blending that has taken place up to this stage will then add still another increment of diffusion to the overall process of obtaining a well-distributed light field devoid of high intensity spots that adversely affect the print. Consequently, when the light passes through the diffusing plate 98 and then through the negative designated by the reference numeral 112, the light is well diffused. This .light, then proceeds downwardly through the bellows 34 and the lens 36, striking the photosensitive paper (not shown) on the top of the table 12.

Due to the detailed description herein given, it is thought that those familiar with the photographic printing art will be able to appreciate the benefits to be derived from a practicing of our invention. It should be'pointed out, though, that each pairof lampssm; 54G"and'54B can be controlled as to its intensity through the agency of variable voltage transformers (not shown) that areadju st ed by'the knobs incorporated into the controls 14. Consequently, if the operator wishes more of a given primary color to be introduced into the mixing chamber 84, he "need o'nly'adjust the intensity of the particular lamps thatwill'either increase or decrease (asc'ircumstances require) the lightener'gy within thespectral range for that particular primary color. it will be appreciated that two 'sets of lamps 54 have been illustrated, one'set being at each end of the rectangular cubicle 38. in this way, the desired color balance is easily achieved in practice.

x We claim:

1. In a photographic enlarger having a lamphouse assembly for directing diffused light through a negative onto a photosensitive surface in making a print from the negative, the lamphouse assembly comprising a plurality of individual light sources providing light energy having different primary colors, first means providing a first chamber for premixing said different primary colors, and second means'providin'g a second chamber for receiving the premixed light and additionally mixing the premixed light, said second chamber having an emission opening via which the mixed light energy is directed onto said surface. a a

2. A photographic enlargerin accordance with claim 1 in which'said second mixing chamber has an upwardly recessed roof at the top and in which said emission openingis located at the bottom. 7

3. A photographic enlarger in accordance with claim 1 including light'dispersing means between said first and second means.

4. In a photographic enlargerhaving a lamphouse assembly for directing diffused light through a negative onto a photosensitive surface in making print from the negative, the lamphouse assembly comprising a main mixing :chamber, a premixing chamber at opposite ends of said 'rfnain mixing chamber, and a pluralityof individual light sources associated with each premixing chamber so as to direct light thereinto, each source providing light energy having a particularly primary color and said main mixing chamber having an emission opening via which the mixed light energy is directed onto said surface.

5. A photographic enlarger in accordance with claim 4 in which each premixing chamber includes first and second walls having reflective surfaces, said walls being parallel with respect to each other and to said emission opening.

6. A photographic enlarger in accordance with claim 5 in which each plurality of light sources includes aset of three lamps arranged at right angles with respect to each other, one lamp directing light directly into the premixing chamber with which it is associated, and each premixing chamber having angularly disposed reflective walls for reflecting light energy from the remaining two light sources into their premixing chamber, said angularly disposed reflective walls being perpendicular to said first and second walls.

7. A photographic enlarger in accordance with claim 6 including a light dispersive means between each premixing chamber and said main mixing chamber.

8. A photographic enlarger in accordance with claim 7 in which said light dispersive means constitutes a rod screen composed of cylindrical segments at each side thereof.

9. in a photographic enlarger having a lamphouse assembly for directing diffused light through a negatiire onto a photosensitive surface in the making of a print from thenegative, the lamphouse assembly comprising a mixing chamber, said mixing chamber including upstanding wall rneans provided with inwardly facing matte reflective surfaces, said wall means having at least one entrance port through ii'hichlight energy is introduced into said chamber, and a roof formed with an upwardly recessed portion provided with a generally downwardly facing matte reflective surface, said mixing chamberhaving an open bottom through which light energy reflected from said surfaces is abstracted and directed onto said surface, and means adjacent said entrance port providing a highly reflective chamber for premixing color light energy to provide the light energy introduced through said entrance port. 7

10. A photographic enlarger in accordance with claim 9 in which said recessed portion is inwardly disposed from the outer edges of said roof. V I

11. A photographic enlarger in accordance with claim 10 in which saidrecessed portion is formed with a pair of upwardly inclined panels and a horizontal panel therebetween.

12. A photographic enlarger assembly in accordance with claim 11 in which said recessed portion is elongated, said inclining panels extending lengthwise along each side of said horizontal panels, and said recessed portion additionally including a pair of upwardly inclining panels at the ends of said horizontal panel.

13. A photographic enlarger assembly in accordance with claim 12 including a horizontal panel section extending inwardly from said outer edges to the lower edges of said upwardly inclining panels.

14. A photographic enlarger in accordance with claim 13 in which the marginal edges of said horizontal section overliethe upper edges of said upstanding wall means.

15. A photographic enlarger in accordance with claim 14 including a plurality of resilient clips engaging said marginal edges to releasably retain said roof in place. a

16. A photographic enlarger in accordance with claim 15 in which said wall means forms an elongated mixing chamber, said one port being disposed in said wall means at one end of said chamber, and said wall means having a second port for introducing additional light energy into said chamber. 7

17. A photographic enlarger in accordance with claim 16 including a second premixing chamber, one premixing chamber being associated with each of said ports, both of said premixing chambers being elongated and having reflective surfaces parallel to each other and parallel to said emission opening.

18. Aph'otographic enlarger in accordance with claim 17 including a rod screen adjacent each of said portsso that light energy introduced into said mixing chamber from said premix ing chambers passes through said rod screens.

19. A lamphouse assembly comprising an elongated mixing chamber, said mixing chamber including upstanding wall means provided with inwardlyfacing reflective surfaces, said wall means having an entrance port at each end through which light energy is introduced into said chamber, a roof formed with an elongated recessed portion having a pair of upwardly inclined panels and a horizontal panel therebetween. said panels providing a generally downwardly facing reflective surface, said recessed portion being inwardly disposed from the outer edges of said roof, and a horizontal panel section ex tending inwardly from the outer edges of the roof to the lower edges of said upwardly inclining panels with the marginal edges of said horizontal section overlying the upper edges of said upstanding wall means, means releasably retaining said roof in place, said mixing chamber having an open bottom through which light energy reflected from said surfaces is ab.- stracted, a premixing chamber associated with each of said ports, and a rod screen adjacent each of said ports so that light energy introduced into said mixing chamber from said premixing chambers passes through said rod screens, and first, second and third light source means for each of said premixing chambers, each source means for each premixing chamber providing light energy of a different primary color, said first light source means in each instance being located so as to direct its light energy into its respective premixing chamber in a direction perpendicular to the general plane of the rod screen associated therewith, and said second and third light source means being located so as to first direct light energy in a direction parallel to the general plane of said rod screens, and angularly oriented reflectors in each premixing chamber 

1. In a photographic enlarger having a lamphouse assembly for directing diffused light through a negative onto a photosensitive surface in making a print from the negative, the lamphouse assembly comprising a plurality of individual light sources providing light energy having different primary colors, first means providing a first chamber for premixing said different primary colors, and second means providing a second chamber for receiving the premixed light and additionally mixing the premixed light, said second chamber having an emission opening via which the mixed light energy is directed onto said surface.
 2. A photographic enlarger in accordance with claim 1 in which said second mixing chamber has an upwardly recessed roof at the top and in which said emission opening is located at the bottom.
 3. A photographic enlarger in accordance with claim 1 including light dispersing means between said first and second means.
 4. In a photographic enlarger having a lamphouse assembly for directing diffused light thRough a negative onto a photosensitive surface in making a print from the negative, the lamphouse assembly comprising a main mixing chamber, a premixing chamber at opposite ends of said main mixing chamber, and a plurality of individual light sources associated with each premixing chamber so as to direct light thereinto, each source providing light energy having a particularly primary color and said main mixing chamber having an emission opening via which the mixed light energy is directed onto said surface.
 5. A photographic enlarger in accordance with claim 4 in which each premixing chamber includes first and second walls having reflective surfaces, said walls being parallel with respect to each other and to said emission opening.
 6. A photographic enlarger in accordance with claim 5 in which each plurality of light sources includes a set of three lamps arranged at right angles with respect to each other, one lamp directing light directly into the premixing chamber with which it is associated, and each premixing chamber having angularly disposed reflective walls for reflecting light energy from the remaining two light sources into their premixing chamber, said angularly disposed reflective walls being perpendicular to said first and second walls.
 7. A photographic enlarger in accordance with claim 6 including a light dispersive means between each premixing chamber and said main mixing chamber.
 8. A photographic enlarger in accordance with claim 7 in which said light dispersive means constitutes a rod screen composed of cylindrical segments at each side thereof.
 9. In a photographic enlarger having a lamphouse assembly for directing diffused light through a negative onto a photosensitive surface in the making of a print from the negative, the lamphouse assembly comprising a mixing chamber, said mixing chamber including upstanding wall means provided with inwardly facing matte reflective surfaces, said wall means having at least one entrance port through which light energy is introduced into said chamber, and a roof formed with an upwardly recessed portion provided with a generally downwardly facing matte reflective surface, said mixing chamber having an open bottom through which light energy reflected from said surfaces is abstracted and directed onto said surface, and means adjacent said entrance port providing a highly reflective chamber for premixing color light energy to provide the light energy introduced through said entrance port.
 10. A photographic enlarger in accordance with claim 9 in which said recessed portion is inwardly disposed from the outer edges of said roof.
 11. A photographic enlarger in accordance with claim 10 in which said recessed portion is formed with a pair of upwardly inclined panels and a horizontal panel therebetween.
 12. A photographic enlarger assembly in accordance with claim 11 in which said recessed portion is elongated, said inclining panels extending lengthwise along each side of said horizontal panels, and said recessed portion additionally including a pair of upwardly inclining panels at the ends of said horizontal panel.
 13. A photographic enlarger assembly in accordance with claim 12 including a horizontal panel section extending inwardly from said outer edges to the lower edges of said upwardly inclining panels.
 14. A photographic enlarger in accordance with claim 13 in which the marginal edges of said horizontal section overlie the upper edges of said upstanding wall means.
 15. A photographic enlarger in accordance with claim 14 including a plurality of resilient clips engaging said marginal edges to releasably retain said roof in place.
 16. A photographic enlarger in accordance with claim 15 in which said wall means forms an elongated mixing chamber, said one port being disposed in said wall means at one end of said chamber, and said wall means having a second port for introducing additional light energy into said chamber.
 17. A photographic enlarger in accordance with claim 16 includiNg a second premixing chamber, one premixing chamber being associated with each of said ports, both of said premixing chambers being elongated and having reflective surfaces parallel to each other and parallel to said emission opening.
 18. A photographic enlarger in accordance with claim 17 including a rod screen adjacent each of said ports so that light energy introduced into said mixing chamber from said premixing chambers passes through said rod screens.
 19. A lamphouse assembly comprising an elongated mixing chamber, said mixing chamber including upstanding wall means provided with inwardly facing reflective surfaces, said wall means having an entrance port at each end through which light energy is introduced into said chamber, a roof formed with an elongated recessed portion having a pair of upwardly inclined panels and a horizontal panel therebetween, said panels providing a generally downwardly facing reflective surface, said recessed portion being inwardly disposed from the outer edges of said roof, and a horizontal panel section extending inwardly from the outer edges of the roof to the lower edges of said upwardly inclining panels with the marginal edges of said horizontal section overlying the upper edges of said upstanding wall means, means releasably retaining said roof in place, said mixing chamber having an open bottom through which light energy reflected from said surfaces is abstracted, a premixing chamber associated with each of said ports, and a rod screen adjacent each of said ports so that light energy introduced into said mixing chamber from said premixing chambers passes through said rod screens, and first, second and third light source means for each of said premixing chambers, each source means for each premixing chamber providing light energy of a different primary color, said first light source means in each instance being located so as to direct its light energy into its respective premixing chamber in a direction perpendicular to the general plane of the rod screen associated therewith, and said second and third light source means being located so as to first direct light energy in a direction parallel to the general plane of said rod screens, and angularly oriented reflectors in each premixing chamber for reflecting light energy from said second and third light source means in a direction perpendicular to the general plane of the particular rod screen associated therewith.
 20. A lamphouse assembly in accordance with claim 19 in which said roof retaining means includes a plurality of resilient clips engaging the marginal edges of said horizontal section and the upper edges of said upstanding wall means. 